DESCRIPTION: (Applicant's abstract) Stimulation of various brain stem areas can initiate and maintain walking in decerebrate animals through the modulation of spinal pattern generators. The applicants have previously described anatomical, functional and neurochemical organizational components of these areas. Information was provided on the elements required for locomotion including progressive movement, rhythm generation, and postural stability. Single unit recording in mesopontine cholinergic cell groups revealed the classes of neurons involved in stepping. These past studies have led to the development of a device for epidural stimulation of the spinal cord which can induce locomotion and respiration. Hypotheses on the organization and modulation of rhythmic functions by the brain stem were also generated by past findings and have led to the present application. Electrophysiological techniques are to be used to address three mechanisms. 1) How these brain stem areas process sensory afferent information in the modulation of ongoing activity as well as changes in state will be addressed. 2) How cholinergic and catecholaminergic cell groups in the region interact in the modulation of rhythmic functions will be studied. 3) How these cell groups modulate reticulospinal efferent systems will be investigated. These studies may provide information relevant to the modulation of locomotor function, sleep-wake states and arousal.